GB2060714A

GB2060714A - Transfer printing sheets

Info

Publication number: GB2060714A
Application number: GB7842443A
Authority: GB
Original assignee: BEMROSE UK Ltd
Current assignee: BEMROSE UK Ltd
Priority date: 1978-09-04
Filing date: 1978-10-30
Publication date: 1981-05-07

Abstract

A method for decorating a textile article in which a dyestuff or pigment is transferred from a carrier onto the textile article under the influence of applied heat and pressure. The dyestuff or pigment is contained in a film-forming polymer on a backing sheet, there being interposed between this layer and the backing sheet a layer containing a component which, under the process conditions, melts and assists the transfer of the dyestuff or pigment layer to the textile article. A preferred component is one which includes N-methylol groups such as N- methylol N'-stearyl urea. The film forming polymer may be an acrylic polymer, for example poly(butyl methacrylate) or poly(isobutyl methacrylate).

Description

SPECIFICATION Transfer printing process This invention relates to transfer printing processes for decorating textile articles.

Known transfer printing processes involve the pre-printing of a paper and the subsequent contracting together of the paper and a textile article under heat afld pressure conditions sufficient to cause dyestuffs in the ink to sublime and transfer to the textile article. Such a process is unsuitable for natural and cellulosic fibres as there is no affinity between the sublimable dyestuffs and the fibres.

A transfer printing process has been proposed for use in decorating textile materials made of natural or cellulosic fibres in which the usual printing ink containing the dyestuffs is replaced by a removable layer located on the paper, the removable layer containing the colourant (pigment and/or dyestuff) and a film-forming polymer. On applying heat and pressure to the paper in contact with the textile article, the film-forming polymer is released from the paper and becomes adhered to the textile article. This transfer may be carried out at a relatively low temperature. Subsequently the textile article is subjected to a heat treatment at a high temperature to fix the colourant on the textile article and to decompose or otherwise dispose of the film-forming polymer so that it does not unduly affect the properties, for instance, handle, of the textile article.

Such a process, although involving the use of a lower temperature than that required for the traditional transfer printing process, nonetheless requires a comparatively high pressure to effect the transfer, such a pressure being achieved by carrying out the transfer on a calender. The two-stage process, involving the transfer of the calender followed by a heat treatment in an oven, is slow and consequently rather inefficient. Furthermore, the resistance to washing and rub fastness of the decorated textile article could desirably be improved.

According to the present invention there is provided a method of decorating a textile article comprising contacting the -article with a dyestuff and/or a pigment carrier and applying heat and a pressure to the resultant combination, the carrier including a backing sheer and first and second layers thereon, the first layer being interposed between the second layer and the backing sheet, the second layer containing the dyestuff and/or pigment and a film-forming polymer, and the first layer including a component which, under the applied heat and pressure, melts and assists the transfer of the second layer to the textile article.

Preferably the second layer includes a suitable catalyst which unblocks above a particular temperature, that temperature being reached during the transferprocess. In this case the component in the first layer should melt at a temperature below the temperature of unblocking of the catalyst.

The component in the first layer should desirably have flow properties, on melting, which enable the component to mix with the second layer and flow into the textile article being decorated.

The manner in which the component in the first layer assists the transfer of the second layer is intended to be understood broadly. Thus the component may assist in the release of the second layer, but it may also assist in the penetration of the second layer into the textile article. The component may itself at least partially transfer to the textile article where reaction may take place with the textile article or with one of the components of the second layer.

By the inclusion of a suitable component in the first layer it is possible to operate the method under a lower pressure than the above-mentioned known method. For instance, transfer can be effected using a pressure in the range of from 1 to 1 0 p.s.i. Such a pressure can suitably be provided by a flat bed press. Alternatively the process can be carried out under a higher pressure on a calender when the dye or pigment achieves better penetration into the textile material and increased rub fastness as compared with the above-described known process.

The present invention also provides a carrier for a dyestuff and/or a pigment, said carrier being suitable for use in the method of the present invention. Furthermore, the invention also provides a precursor for said carrier, said precursor including the backing sheet and the first layer but not having the second layer applied thereto.

When used herein, the term textile article is intended to cover any textile fabric or other material (e.g. non-woven fabric) which may suitably be decorated by methods used for textile articles. Articles made of both natural and synthetic fibres or blends thereof may be decorated and, for instance, the method of the invention is applicable to articles such as panels for T-shirts made of cotton.

The first layer may be in the form of a wax/resin coating, preferably including a film-forming polymer, more preferably an acrylic polymer and most preferably a polybutyl methacrylate, for instance, polyisobutyl methacrylate.

The component in the first layer may be a waxy substance having groups which are able to react, under the temperature conditions of the process, with the surface of the textile article being decorated and/or the cross-linking agent which may be present in the second layer (referred to below). Preferably the component includes N-methylol groups. A preferred component is an N-methylol urea of the formula

where R is a long chain group, for instance, a fatty acid residue such as stearic, C17H3sCO. Such a component may be, for instance, the reactive water-proofing agent known as Persistol HP.

Other materials which may be of use in the present invention are the following water-proofing agents: Permel B, BIP BT323, Vialan NW a N (manufactured by l.C.I. Limited), Phobotex FTS a FT (manufactured by Ciba-Geigy), Mystocks, Cerol EWL (manufactured by Sandoz).

Although the relative proportions of the film-forming polymer and the N-methylol component in the first layer may be varied from one system to another, the relative proportions in any one system are likely to be variable only within small limits. For instance where the film-forming polymer is a polybutyl methacrylate and the N-methylol component is a urea of the above formula in which R is stearic in the form of the commercially available water-proofing agent Persistol HP, then approximately equal amounts by weight of the emulsions containing these components has proved satisfactory.

Furthermore, the presence of excess Persistol HP has resulted in a decorated textile material having less good west fastness. Equally too much polybutyl methacrylate has resulted in insufficient release of the second layer to give a good product. It will be appreciated that the proportions used will depend on the solids content of the emulsions from which the first layer is prepared.

A suitable press for a method in accordance with the present invention is a conventional flat bed platen type press currently used for sublimation type transfer printing processes referred to above. Such presses given an even pressure of between 1 and 10 p.s.i. over the buck area and can be heated to maintain a temperature of from 30 to 250"C. For the process of the invention, the pressure, temperature and time for the transfer will vary according to the nature of the fabric or other material being decorated, but will normally be within the ranges from 1 to 10 p.s.i., from 1200 to 2100C and from 10 to 90 seconds.The method may be carried out as a single stage process in which the carrier and the textile article are contacted together, for instance, in the flat bed press, long enough for the second layer to be transferred and also to be fixed to the textile article. Alternatively the dwell time within the pressure may be sufficient for the transfer to take place, the fixing or the completion of the fixing being effected subsequently by a further suitable heating stage sufficient to effect a cure of the transferred decorating layer, for instance, by heating the textile material in a suitable oven.

The first layer should be of substantial thickness and during the process a portion of the first layer is transferred along with the second layer so that in effect the first layer actually splits, part remaining on the backing sheet and part transferring with the second layer.

The first layer can be applied by any method which produces an even film having a weight of between 5 and 30 g.s.m. (grams per square metre). Examples of such methods include air-knife coating, silk screen printing, gravure printing, roller coating and spray coating.

The second layer may be similar to the removable layer described in U.K. patent specification No.

1 ,496,89 1. Preferably the film-forming polymer in the second layer is polyvinyl butyral and the layer also contains a cross-linking agent such as a dimethylol urea as well as a plasticizer and a catalyst.

The second layer may be applied by any suitable printing process, for instance, gravure, flexographic flat and rotary screen lithographic and dry offset printing.

The backing sheet to which the layers are applied may be a single sheet of a size suitable for application to a single textile article such as a T-shirt. Alternatively it could be a long length of material such as a roll of paper. In the latter case the first and second layers may be applied to the backing sheet by means of a continuous printing process, and the application of the first layer may be carried out at the first head of the printing process, the second layer being applied at the second and subsequent heads of the process.

In a particularly preferred method the first layer contains polyisobutyl methacrylate and Nmethylol N'-stearyl urea and the second layer contains polyvinyl butyral together with a suitable crosslinking agent, a plasticizer and a catalyst.

An example in accordance with the present invention will now be described.

A composition was prepared by mixing together equal parts by weight of polyisobutyl methacrylate (Surcol 520 -- an emulsion with 40% solids) and stearic substituted N-methylol urea (Persistol HP - an emulsion containing 40 to 50% solids). The resultant waxlresin composition is applied as a coating in an amount of approximately 20 g.s.m. (grams per square metre) to a blade coated M.F. paper by means of an air-knife paper coating machine. The coated paper is then dried by warm air.

The resultant wax/resin coated paper is then silk screen printed on a flat bed silk screen printing press with an ink having the following formulation: Pigment 5% Polyvinyl butyral resin 15% Wax plasticizer (Cirrasoi ALN-WF) 10% Substituted dimethylol propylene urea (Fixapret PCLS) 4% Catalyst (blocked PTSA) 0.2% Solvent (50/50 diacetone alcohol/polyethylene glycol) 65.8% The ink is then dried by warm air at 60"C.

A textile article made of interlock cotton is then placed on a flat bed platen press and the dried printed paper is then placed in contact with the textile article. The press is operated for thirty seconds at 2000C at a pressure of 6 p.s.i.

The resultant print on the textile article gives a wash-fast result of commercially acceptable quality.

The mechanism by which the methylol urea in the first layer assists the transfer of the second layer is not fully understood. The methylol urea has a low melting point and also has release properties.

it is a water-repellent, softening agent and the resultant decorated textile article has good handle as well as good rub fastness. Investigations have been carried out using scanning electron and visual microscopical analysis, film casting of ink and release film components, melting point estimate and determinations of the water absorbency of the resultant prints, and it is believed that the following stages take place during the transfer process: Stage 1.

As the transfer paper/fabric combination is heated up to its maximum temperature (1900 C) the release film melts (70 to 900 C) and allows the ink and release film remnants to move, by gravity to the surface of the fabric. it is probable that at this stage the initial mixing of release film and ink components takes place.

Stage 2.

As the temperature is raised still further more flow and further mixing of the ink and release film component takes place, untii at a temperature of 1400C the blocked catalyst (PTSA) unblocks, becomes active, and initiates the cross-linking reactions.

It may be that under the temperature and pressure conditions of the process that Persistol HP reacts directly with the cotton surface and also through the cross-linking agent, Fixapret PCLS, according to the scheme represented diagrammatically below: Cotton Fabric Surface

The reaction involving the Fixapret PCLS only takes place in the areas where the printing ink is present.

Although the above mechanisms are undoubtedly not the only ones operating in the complex transfer process, it may well be that they are responsible for the improved properties of the transfer print, including penetration, improved rub fastness and wash resistance.

Claims

1. A method of decorating a textile article comprising contacting the article with a dyestuff and/or a pigment carrier and applying heat and a pressure to the resultant combination, the carrier including a backing sheet and first and second layers thereon, the first layer being interposed between the second layer and the backing sheet, the second layer containing the dyestuff and/or pigment and a film-forming polymer, and the first layer including a component which, under the applied heat and pressure, melts and assists the transfer of the second layer to the textile article.

2. A method according to claim 1 wherein the second layer includes a suitable catalyst which unblocks above a particular temperature, that temperature being reached during the transfer process.

3. A method according to claim 1 or claim 2 wherein the component in the first layer has flow properties, on melting, which enable the component to mix with the second layer and flow into the textile article being decorated.

4. A method according to any of the preceding claims, wherein the first layer is in the form of a wax/resin coating including a film-forming polymer.

5. A method according to claim 4 wherein the film-forming polymer is an acrylic polymer.

6. A method acording to claim 5 wherein the acrylic polymer is a polybutyl methacrylate.

7. A method according to claim 6 wherein the polybutyl methacrylate is polyisobutyl methacrylate.

8. A method according to any of the preceding claims wherein the component in the first layer is a waxy substance having groups which are able to react, under the temperature conditions of the process, with the surface of the textile article being decorated and/or the cross-linking agent which may be present in the second layers.

9. A method according to any of the preceding claims wherein the component in the first layer includes N-methylol groups.

10. A method according to any of the preceding claims wherein the component in the first layer is an N-methylol urea of the formula

where R is a long chain group 1 A method according to claim 10 wherein R is a fatty acid residue.

1 2. A method according to claim 11 wherein R is a stearic group.

13. A process according to any of the preceding claims wherein the film-forming polymer in the second layer is polyvinyl butyral.

14. A process according to any of the preceding claims wherein the second layer also contains a dimethylol urea.

1 5. A method according to claim 1 and substantially as herein described.

1 6. A method of decorating a textile article substantially as described in the specific example.

1 7. A carrier for a dyestuff and/or a pigment, the carrier being suitable for the process of any of the preceding claims and including a backing sheet and first and second layers thereon, the first layer being interposed between the second layer and the backing sheet, the second layer containing the dyestuff and/or pigment and a film-forming polymer, and the first layer including a component which, under the applied heat and pressure, melts and assists the transfer of the second layer to the textile article.

1 8. A precursor for a carrier as claimed in claim 1 7, said precursor including the backing sheet and the first layer but not having the second layer applied thereto.